Electrolytic polishing



Jan. 8, 1952 5 B, EMERY 2,582,020

ELECTROLYTIC POLISHING Filed July 15, 1947 v 2 SHEETS-SHEET 1 INV R. ESHLT-LOOA/B. EBY ,MEZA

Jan; 8, 1952 r 5, EMERY 2,582,020

- ELECTROLYTIC POLISHING Filed July 15, 1947 2 SHEETS-SHEET 2 INVENTOR. I

. BY a 74 21m 6.

Patented Jan. 8, 1952 ELECTROLYTIC POLISHING- Sheldon B. Emery, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 15, 1947, Serial No. 760,951

3 Claims.

1 v This invention relates to electrolytic polishing and deburring and is particularly concerned with operations on cupreous metals and the like.

It is therefore a primary object of this invention to provide a method and apparatus for electrolytically polishing and deburring cupreous articles.

In carrying out this object, it is another object of the invention to utilize alternating current as a power source for the electrolytic bath.

A still further object of the invention is to provide an apparatus for carrying out the method wherein a cathode is utilized which has a dual function of acting as a cathode in the electrolytic polishing bath and simultaneously acting as a rectifier for changing the alternating current to effective direct current.

In carrying out the above object, it is another object to utilize a film-forming metal as a cathode, for example, aluminum, tantalum or magnesium.

A still further object of the invention is to provide an electrolyte for use in the method which has a low factor of dissociation and which does not attack the film on the cathode. In some cases, it may be desirable to add a brightener to the bath, such as a polyhydric alcohol.

Another object of the invention is to provide a method for electrically connecting several polishing baths to a single transformer wherein the efliciency of the setup is improved by utilizing both half waves of the alternating current.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

Fig. 1 shows a sine wave indicating an A. C. current, the shaded portions having similar polarity, being that part of the current that is used in the cell hookup shown in Fig. 2.

Fig. 3 shows a sine wave indicating an A. C. current wherein the shaded portions above the axis are used in one cell and the shaded portions below the line'are used in the other cell hookup shown in Fig. 4.

Fig. 5 shows two sine waves superimposed wherein the shaded portions of the A C. current 2 are alternately used in the two cells shown in the hookup, Fig. 6. I

Electrolytic polishing and deburring is a Well known expedient for use with various metals. In the usual type of apparatus, a cathode is utilized as one electrode in the electrolytic bath and the work to be polished is connected in the circuit as the anode. An electrolyte is provided which will suitablypolish and debur the material being operated upon and in most cases, contains phosphoric acid together with desired quantities of sulphuric acid. The current source for such operations is direct current, provided by a motor-generator set or other suitable apparatus. The necessity of direct current is one of the expensive items in electrolytic polishing procedures since this type of current is not usually available and requires a motor-generator setfor its production.

This invention is directed to a method and apparatus for electrolytically polishing cupreous materials, for example, brass, bronze, berylliumcopper and in fact any copper alloy wherein the copper predominates. In this respectystainless steel and the like may be polished if sufficiently high current densities are utilized. The main advantage of the apparatus and method is that alternating current is used as the power source and in this manner current may be taken from any alternating current source.

In use, the A. C. current must be rectified and this is accomplished by providing a cathode in the electrolytic polishing bath which may be filmed or anodized. The cathode may be filmed prior to its introduction into the bath, or the film may be formed during the first polishing operation. This film or anodized coating-permits current fiow in one direction but not in'the other whereby in a single cell setup, as shown in Fig. 2, the half waves of the current (those of the same polarity as shown in Fi 1) only are utilized. Thus it'is possible to merely connect a transformer to an alternating current power line and utilize the current from this transformer in the polishing cell.

I have found that it is important to utilize electrolytes that do not attack the film on the aluminum or other anodized metal. For this reason, I prefer to use as a base for the electrolyte, acid having a very low factor of dissociation such as citric acid, tartaric acid, etc. To this acid or salt thereof is added a salt of a strong acid and a weak. base for example, ammonium phosphate or the like. A brightener in the form of glycerine, ethylene glycol or other polyhydric alcohol may be added if desired together with a large quantity of water. Several specific formulas for the electrolyte are as follows:

#1. A saturated solution of ammonium phate.

#2. A saturated solution of ammonium phate and 5% phosphoric acid.

#3. A saturated solution of ammonium phate and 5% to 50% citric acid.

#4. A saturated solution of ammonium phate and 5% to 50% tartaric acid.

#5. Ammonium citrate in saturated solution with 5% phosphoric acid- 100 grams ammonium phosphate 100 grams citric acid 25 grams potassium phospha 1000 cc. water Current densities from one-half ampere to four amperes per square inch have been found to be satisfactory. and it is :noted:v that thetime of polishing is inversely proportional tothei-current density; for'example, at one-half ampere satisfactory polishing'o'ccurs in about two minutes whereas at four amperes, a thirty second immersion is satisfactory. .Inalljinstances, the :voltage usedmust bevaried in-:accordance with'the distances-between the electrode for best results and I have found that from six to twenty-five volts gives very satisfactory'results.

When polishing cupreous 'alloys,'a deposition of loose copper is sometimes noted on the aluminum cathode during :periodseofbath idleness; This may be brushed off if desired or: the cathode may be removed from. the bath during periods of idleness, in any eventthedeposit'hasno deleterious eiIect on the operation. 'In all cases, the electrolyte has a dual purpose of acting as a' polishing medium by a slight dissolution of the metal to be polished and simultaneously acting as an anodizing. means for'the aluminum or other cathode metal provided. r v 'Various electrical hookups may be resorted to for obtaining different efiiciencies or operation and these will be'noted by referring to the drawings, wherein, in all drawings, 20 indicates a phosphosphostransformer connected to an A: C. power source.

The output of the transformer is lead to electrodes 25 and 28. In all cases, 26 is a filmed electrode such as aluminum and :28 is the work to be polished. The electrodesZE and 28 are contained in cells 22 which are substantially'filled with suitable electrolyte. Y

The sine wave preceding each cell hookup indicates the portion of the current used in the parti'cular'setup as noted by shaded lines. Whilethe embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming withinthe scope of the claims which follow.

phosv What is claimed is as follows:

1. In a method for utilizing alternating current in electrolytic polishing operations, the steps comprising; providing a cathode taken from the class consisting of aluminum, tantalum and magnesium, positioning the cathode in a cell containing a polishing solution consisting essentially of an electrolyte taken from. the class consisting of a saturated aqueous solution of ammonium phosphate, a saturated aqueous solution of ammonium phosphate mixed with a 5 to 50% citric acid solution, and a saturated aqueous solution of ammonium phosphate mixed with-a 5 to 50% tartaric acid solution, providing work to be polished consisting of cupreous metals, and placing said work in the cell as an anode, and then supplying alternating current to the cell by conh through the electrolyte for polishing the work.

2. The method as claimed in claim 1 which includes the added step of connecting the transformer across the electrodes of one cell and connectingsaid cell in series to another cell for utilizing the full current from said transformer whereby the current of one polarity activates one cell and the current 'of the opposite polarity activates the other cell.

3. In a method for electropolishing cupreous metal work pieces, the steps comprising, providing a cathode taken from the class of metals consisting of aluminum, tantalum and magnesium, placing the cathode in a cell containing an electrolyte consisting essentially of 'parts ammonium phosphate, 100 parts citric acid, '25 parts potassium phosphate and 1000 parts water, providing a cupreous metal workpiece to be polished and placing same in the cell to be used as the anode and then'supplying alternating current to the cell by connecting the output of a transformer to said cathode and to said anode whereby the cathode films, permitting only unipolarity current to iiowthrough electrolyte for polishing the cupreous workpiece.

, SHELDON B. EMERY.

REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number OTHER REFERENCES Standard Handbook for Electrical'Engineers, by Fowle, published in 1933,"page 996. v 

1. IN A METHOD FOR UTILIZING ALTERNATING CURRENT IN ELECTROLYTIC POLISHING OPERATIONS, THE STEPS COMPRISING; PROVIDING A CATHODE TAKEN FROM THE CLASS CONSISTING OF ALUMINUM, TANTALUM AND MAGNESIUM, POSITIONING THE CATHODE IN A CELL CONTAINING A POLISHING SOLUTION CONSISTING ESSENTIALLY OF AN ELECTROLYTE TAKEN FROM THE CLASS CONSISTING OF A SATURATED AQUEOUS SOLUTION OF AMMONIUM PHOSPHATE, A SATURATED AQUEOUS SOLUTION OF AMMONIUM PHOSPHATE MIXED WITH A 5 TO 50% CITRIC ACID SOLUTION, AND A SATURATED AQUEOUS SOLUTION OF AMMONIUM PHOSPHATE MIXED WITH A 5 TO 50% TARTARIC ACID SOLUTION, PROVIDING WORK TO BE POLISHED CONSISTING OF CUPREOUS METALS, AND PLACING SAID WORK IN THE CELL AS AN ANODE, AND THEN SUPPLYING ALTERNATING CURRENT TO THE CELL BY CONNECTING THE OUTPUT OF A TRANSFORMER TO SAID CATHODE AND SAID ANODE, WHEREBY THE CATODE FILMS AND PERMITS ONLY UNIPOLARITY CURRENT TO FLOW THROUGH THE ELECTROLYTE FOR POLISHING THE WORK. 